The invention relates to a reactor system comprising a reactor chamber having a circumscribing wall, a particle separator adapted to receive a particle-gas suspension from the reactor chamber and means for returning the particles separated by the particle separator to the reactor chamber, which system is here called a circulating fluid bed reactor.
Circulating fluid bed reactors are getting more general in energy technical applications, because in those, discharges of sulphur and nitric dioxides can at low cost be reduced to levels set by government regulation. When burning materials containing especially sulphur, the economic competitiveness of a circulating fluid bed reactor is excellent, when the caloric capacity of the arrangement is less than 200 MW. This limit of capacity will undoubtedly rise, when the technological readiness and experiences from bigger units increase.
In energy technical applications, the purpose of the burning in the first place is to produce heat energy, which shall be transferred further to the coolant of the reactor, which coolant most generally is water. Therefore, the walls of the reactor chamber are usually made of gas tight panels formed of cooling pipes and fins connecting the pipes. On the other hand, it has traditionally been necessary to build the particle separators and the return equipment for solids as an uncooled construction by insulating the supporting structure made of steel with inner ceramic insulators from hot particle-gas suspension. The advantage of this construction is that both the reactor and the particle separator are simple as such and a good deal of experience has already flown in from their ability to function. On the other hand, the whole reactor unit consisting of these components of entirely different structure is not adapted to this purpose.
The biggest problem of the construction described is to connect components with different heat expansion with each other. The massive particle separator, the ceramic parts of which have a thickness of approximately 300 mm, must be supported on the bottom level and provided with a self-supporting jacket of steel. The reactor portion of panel construction is preferably supported from above, whereby it is heat-expanding mainly downwards. Especially in big units, a cooling portion supported from above is the only possibility to be considered. In the fired condition, the typical temperature of a cooled panel structure is about 300.degree. C., while the temperature of the steel jacket of the particle separator is 80.degree. C. at the most, both for safety reasons and to control heat losses. Thus, it is clear that in transient heating and cooling situations, the fastening points of the reactor portion and the particle separator move remarkably with respect to each other. These movements occuring in three vertical directions must be considered when planning structure for their connection.
Another significant disadvantage of a conventional circulating fluid bed reactor is its great bulkiness, because the particle separators having mainly the same dimensions as the reactor portion are located at an unnecessary distance from the reactor portion.
The location of the particle separators far from the reactor chamber causes another disadvantage at the same time. The return equipment shall attend to a horizontal transportation of solids from the middle axis of the separator back into the reactor. Therefore, for the return channel system, complicated equipment for adjusting the gas flow must be provided, which equipment most usually is carried out by means of a separate fluidized bed located in the return channel.
In addition to the inconveniences described above, a conventional circulating fluid bed reactor is unnecessarily expensive and exposed to damage. Especially the junctions between the reactor and the particle separator need regular care.